A piezoelectric/electrostrictive membrane sensor can be used for measuring fluid characteristics such as viscosity, density, and concentration by use of the electromechanical converting function of a piezoelectric/electrostrictive element in which a membranous piezoelectric/electrostrictive body disposed in the sensor is sandwiched between a pair of electrodes. When the piezoelectric/electrostrictive membrane sensor (the piezoelectric/electrostrictive element) is vibrated in a fluid, the sensor meets with a mechanical resistance caused by the viscosity resistance of the fluid, and the electric constant of the piezoelectric/electrostrictive element changes in a certain relation with respect to the mechanical resistance. Therefore, the sensor can detect the constant to measure the viscosity of the fluid.
It is to be noted that no prior document having the same object as or an object in common with the object of the present invention described below seems to be present, however examples of a prior document for reference of the piezoelectric/electrostrictive membrane sensor include Patent Documents 1 to 6.
Patent Document 1: JP-A-8-201265
Patent Document 2: JP-A-5-267742
Patent Document 3: JP-A-6-260694
Patent Document 4: JP-A-2005-164495
Patent Document 5: JP-A-2-51023
Patent Document 6: JP-A-8-98884